1. Field of the Invention:
The invention relates to an instrument for reducing or repositioning and fixing of pertrochanterous and subtrochanterous fractures, comprising at least one arcuate bone nail of elastic material, said nail being bent at least at its proximal end portion and being insertable into the medullary canal of the bone via an impact hole arranged in the bone proximally of the knee joint and, in view of its elasticity, contacts under tension with the apex of the bent portion the wall, opposing the impact hole, of the medullary canal and is provided at its distal end with a coupling member allowing on all sides a positive connection for rotation with an impact tool. The invention further relates to an insert member forming part of this instrument.
2. Discussion of the Prior Art
It is already known to reduce or reposition and to fix pertrochanterous and subtrochanterous fractures by opening the bone to form an impact hole and by introducing into this impact hole at least one bone nail, conveniently several bone nails, consisting of elastic material and being bent at least in its proximal area. When introducing such bone nails into the medullary canal, the nails contact, in view of their elasticity, with the apex of the arcuate portion under tension the wall, opposing the impact hole, of the medullary canal. It may be noted that if the proximal point of each nail arrives at the area of the fracture, the nail is passed beyond this fracture and enters the condyle of the bone and is fixed to the fractured area. By rotating the individual nails, the bone portions can be reduced such that they assume the correct relative position at the area of the fracture. For this purpose, the distal end of each nail is provided with a coupling member allowing a wholly non-rotational connection with an impact tool. It is already known to give this coupling member the shape of a small plate-like flattening, but also other embodiments of the coupling member are possible. With the known nails assuming correct position within the medullary canal, the nail ends protrude from the impact hole and the coupling member contacts under tension the outer surface of the bone distally of the impact hole, so that there exists, particularly with older persons having porous bones, the danger that the bone may collapse at the contacting area and additionally the sinews and muscles extending above the impact hole are irritated by the protruding distal nail ends.
As a rule, the impact hole is made such that the bone is first punctured and subsequently the small hole thus formed is widened by means of a three- or four-edged reamer, enlarged by means of a chisel or by means of a drill. In all these cases, parts of the bone can be split off thus enlarging the impact hole in an undesired manner. But also when forcibly driving the nails, a cortical wedge can be split off the proximal cortex by the tangential shearing stress, which results to an undesired enlargement of the impact hole, noting that the edge of the impact hole can also collapse at the forward side. Both cases result in the nails protruding in an uncontrolled manner and, if the fracture extends into the bone, a torsional fracture of the thigh might be produced by the surgeon.
It can also occur that the bone nails are driven too far into the impact hole, so that the coupling member no longer contacts the outer surface of the bone or that the coupling member contacting the outer surface of the bone becomes shifted in direction to the interior of the bone because part of the edge of the hole has been broken away.
If the coupling member enters the interior of the medullary canal and thus disappears within the bone, there results at any rate the drawback that the required tension stress of the nails becomes reduced and that the desired effect is no longer obtained thereby. If the whole nail is located within the medullary canal it might occur that the nail is caught by the spongiosa bubbles present within the medullary canal and is then hindered from sliding in distal direction. If in such a case the bone is loaded such that the bone portions are brought into closer proximity at the area of the fracture it might occur that the nail tip perforates the condyle of the bone and penetrates the socket of the hip joint (acetabulum). If nails having wholly entered the medullary canal are not caught by the spongiosa bubbles, the nails slide in the distal direction and can then be removed only with extreme difficulties. For removing such nails it is at any rate necessary to enlarge the impact hole to such an extent that the distal end located within the medullary canal can be seized.